Solomon Islands

Earthquake
Hazard level:
High

In the area you have selected (Solomon Islands) earthquake hazard is classified as high according to the information that is currently available. This means that there is more than a 20% chance of potentially-damaging earthquake shaking in your project area in the next 50 years. Based on this information, the impact of earthquake must be considered in all phases of the project, in particular during design and construction. Project planning decisions, project design, and construction methods should take into account the level of earthquake hazard. Further detailed information should be obtained to adequately account for the level of hazard.

Recommendations

EARTHQUAKE HISTORY AND HAZARD: Get information about major earthquakes and secondary hazards (fires, landslides, liquefaction, tsunami in coastal areas) that have affected the project area in the past and the effects these caused. Community memory and historical accounts of earthquakes can provide useful information to supplement scientific studies.
Contact the governmental organisations (e.g. Ministry of Environment and Geological Survey/ Ministry of Earth Sciences) responsible for earthquake risk management in the project country to obtain more detailed information on the potential earthquake hazard.
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Understanding the earthquake history of any place is important to acknowledge the possibility that an earthquake can affect the region again and also to consider the extent of possible damage. While the latter is a function of the vulnerability of the built environment, the former informs us of the prevalent hazard, especially in regions with a history of earthquakes.

In many countries, earthquake history can be obtained from written historical records. It may seem unlikely that a large earthquake would take place hundreds of kilometers away from a tectonic plate boundary in areas with low levels of strain on the crust from tectonic motion. But such earthquakes have happened in the past, and understanding the earthquake history of a place is important before determining a location for a project and initiating the design of the structures.

Community memory and historical accounts of earthquakes can provide useful information to supplement scientific studies. Recording of earthquakes using scientific instruments began only around 1900. In many areas, centuries may pass between major earthquakes, meaning that instrumental records provide an incomplete picture of the hazard. Scientists who study earthquakes use other tools: they investigate faults where earthquakes occur, measure the slow movement of tectonic plates, and search for geologic traces left by ancient earthquakes.

Most countries that fall within earthquake hazard zones have maps that show how strong scientists expect earthquake shaking to be throughout the country. The building code or regulations for earthquake resistant design typically contain these maps, or they may be available from the government agency responsible for earth science or emergency management. Building code hazard maps provide sufficient information to properly design ordinary buildings and other typical structures. For critical facilities such as major dams, power plants, or major hospitals, a more detailed analysis should be done to determine the expected level of earthquake shaking at that particular site. Engineers need this additional information to design the facility properly.

Earthquakes can cause secondary hazards that include fires, landslides, liquefaction (see definition below), floods (can be triggered by failing dams and embankments, glacial lake outbursts, or by landslide-blocked rivers) and tsunami in coastal areas. Obtain information on these hazards from the government agency responsible for emergency management. Maps may exist that describe the extent of tsunami inundation, liquefaction, or land-sliding. Historical records may also contain accounts of secondary hazard events triggered by past earthquakes. Learning about potential tsunami hazard is essential in coastal areas with high earthquake risk.

Liquefaction takes place when loosely packed, saturated sediments at or near the ground surface lose their strength in response to strong ground shaking, and flow like a thick fluid. This can result in major damage during earthquakes. (More details at http://www.usgs.gov/faq/categories/9829/3301). Liquefaction occurs up to a certain depth of the soil and hence if we are able to pre-determine the potential and the possible depth of liquefaction, building foundations can be designed to go below the liquefiable depth and can remain unaffected in earthquake shaking. Knowing the height of the water table in the soil helps us determine its liquefaction potential, the viability of sub-soil floors and housing of critical utilities in such areas.

Earthquakes triggered or induced by human activity are not included in these hazard levels. Instances of 'induced seismicity' and its causes are recorded at http://inducedearthquakes.org/ .

LOCAL BUILDING REGULATIONS: Find out if the local building regulations provide for earthquake protection. To do this, engage the local engineering community, especially those serving with the local government or consult external experts. If regulations do include earthquake protection, comply with the regulations with respect to planning, design and construction, including typology of construction, and materials of appropriate quality suitable for use in areas of low seismic hazard. If they do not, consider adopting and complying with standards from other low earthquake hazard areas.
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Building standards, often called building codes, provide the first line of defense against potential earthquake damage and help to ensure safety in buildings designed and constructed in conformance with the codes. It is important to find out if the local building regulations provide for earthquake protection in the project location. If they do, then comply with the regulating provisions with respect to planning, design and construction, including typology of construction and quality materials for use in areas of seismic hazard.

Reviewing local building regulations is essential for setting the standards for planning, design and construction. Similarly, it is necessary to determine to what extent these regulations take into consideration the earthquake hazard in the region, and whether they provide sufficient protection. To do this, engage the local engineering community, especially those serving with the local government, in discussions. However, in regions where it is felt that local engineers’ capacities are low, consider consulting with external experts who understand the building standards needed in high earthquake hazard zones.

Similarly, it is necessary to understand when these standards were last revised, and how often revisions occur. Earthquake information and engineering developments are rapid, and standards that have not been revised for more than five years may not meet requirements for project design. In such cases, more stringent design standards may have to be followed.

Many provisions in the building standards, if implemented, are intended to ensure that structures can adequately resist seismic forces during earthquakes. Building standards in some parts of the world are based on the required performance of a particular building in a future earthquake event. The performance levels could range from a building designed to prevent collapse in earthquakes, to a slightly improved ‘life safety’ (typically used for ordinary buildings), to ‘immediate occupancy’ where a building is designed to be usable minutes after an earthquake. It should be understood however, that the costs will increase substantially for higher performance levels. Hence, if such standards are in use in the project area, it is essential to understand and consider the performance required for each building in the project, and to set the building-performance goal needed for each. ‘Design Considerations’ provides further detail.

According to the building standards in some countries, the design will be influenced by how important the building is. Importance depends on the functional use of the building, the hazardous consequences of its failure, its post-earthquake functional needs, historical value, occupancy and/or economic importance. An Importance Factor (say 1.5) is multiplied in the calculations to provide additional earthquake resistance to buildings of greater significance. This however, is still an indirect approach. More direct and better approaches are also available for important facilities (see Design Considerations).

If the local building codes do not reflect the seismicity of the area, consider adopting and complying with building standards from other regions sharing similar geological conditions and earthquake hazards. In many countries, seismic hazard is not considered in building standards either because these are rare events or because the earthquake history is incomplete. However, it should be remembered that rare events can happen within the lifespan of the building and result in large losses.

More Information:
The Importance of Building Codes in Earthquake-Prone Communities: http://www.fema.gov/media-library-data/1410554614185-e0da148255b25cd17a5510a80b0d9f48/Building%20Code%20Fact%20Sheet%20Revised%20August%202014.pdf

INTERACTING HAZARDS: Determine whether the project site is likely to be affected by ground failure or other site hazards during an earthquake. Soil investigations should be conducted by a geotechnical engineer to determine physical properties of the soil including its liquefaction potential, the stability of natural slopes and other considerations for design. Select a project location with minimal site hazards if possible. Ensure that the proposed project is not built on or near active earthquake faults.
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Understanding the geology of the project site is one of the first steps in the design process. One needs to determine whether the project site is likely to be affected by ground failure or other site hazards during an earthquake. Maps showing landslide hazard, liquefaction potential (defined below), shaking amplification due to soft soil, and active fault zones may be available. Sometimes these maps are part of a seismic microzonation study report, or they might be available from the government earth science agency.

The foundation is the lowest part of a building which interacts with the soil and transmits the load of the structure to the soil below. Before a foundation type is decided, it is necessary to understand the characteristics of the soil at the site of construction. This is done by soil investigations which should be conducted by a geotechnical engineer who will test the soil at the site and will prepare a report that indicates physical properties of the soil, its bearing capacity, chemical composition, its liquefaction (see below) potential, the stability of natural slopes and other considerations for design. The soil properties can vary from place to place and from layer to layer, even within the proposed project. It is thus very important for projects to undertake these tests, as buildings based on unfavorable soils can experience excessive ground motion or be subjected to the effects of liquefaction and ground failure. The results of the soil studies and their analysis will be used by structural designers to design the foundations and structural elements required for earthquake resistance of the buildings.

Site Hazards: Make sure to select sites with minimal site hazards if possible. Ensure that the proposed project is not built on or in close proximity to active earthquake faults. The project site should not be exposed to falling rocks and landslides from nearby mountains. The presence of large rocks that may have fallen from nearby mountains several years back is a good indication that there is a rockfall hazard.

Liquefaction takes place when loosely packed, saturated sediments at or near the ground surface lose their strength in response to strong ground shaking, and flow like a thick fluid. This can result in major damage during earthquakes. (More details at http://www.usgs.gov/faq/categories/9829/3301). Liquefaction occurs up to a certain depth of the soil and hence if we are able to pre-determine the potential and the possible depth of liquefaction, building foundations can be designed to go below the liquefiable depth and can remain unaffected in earthquake shaking. Knowing the height of the water table in the soil helps us determine its liquefaction potential, the viability of sub-soil floors and housing of critical utilities in such areas.

TECHNICAL EXPERTISE: Engage qualified and experienced local (or international) technical professionals: structural and geotechnical earthquake engineers, and geologists specializing in hazards. Ensure that design and implementation of all project activities, including infrastructure construction and improvements, provide for earthquake protection and comply with local and/or international building standards.
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In most earthquakes, building collapses cause the majority of deaths and injuries. Building standards help to ensure safety of constructions. It is important for the technical personnel involved in building projects in earthquake-prone areas to understand all provisions in the building standards, and also why these are necessary to design and build earthquake resistant structures. They must understand the demands induced during earthquake shaking in the various building components and design measures to counter them so that loss of life and damage to property can be limited.

Sound technical advice is essential to ensure project structures can resist multiple hazards. For project structures to have adequate earthquake resistance, the technical personnel involved must also have relevant experience and expertise in conceptualizing, designing and constructing earthquake resistant structures. Designing and building large structures is always a challenge, and that challenge is even greater when they are built in earthquake-prone areas. Earthquake engineering requires additional technical skills than ordinary structural engineering. All projects in areas of high earthquake hazard should engage the services of technical personnel with knowledge and experience in constructing earthquake resistant structures. It is also important that the team contain geologists who specialize in applying geology to engineering projects, commonly called engineering geologists, in order to better understand current geological processes, the earthquake potential and threat of secondary geologic hazards.

It will be useful to contact local or international experts that have prior experience working in the project area to understand how they sought to reduce earthquake risk in past projects. These experts may be in private consulting practice, in the government, or in universities.

DESIGN CONSIDERATIONS: Set design standards for each building based on the criticality of the functions it shall serve and the building standards applicable in the area. Determine the performance requirements of each structure in the project and design accordingly. For the most vital buildings or infrastructure in the project, higher design standards may be necessary.
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While designing a project in an area of high or medium earthquake hazard, it is important to set standards for the design of each structure which match the importance of the structure’s function (e.g. the emergency department building within a hospital complex, or a bridge on a major highway). When calculating performance requirements, consider how collapse, serious damage, or functional losses of project- associated infrastructure could affect the local population and environment. Also, it is obligatory to follow the building standards applicable in the area and all basic cost estimates will consider design to these standards. It is also important to ensure that there is good quality control and strict adherence to prescribed standards of construction materials and construction processes during the construction. Regular testing of construction materials, periodic training of workmen, and on-site evaluation of the technical work are important elements of good quality control. Good materials and quality construction have benefits beyond earthquake safety, because they reduce maintenance costs.

Several modern international building codes have now adopted Performance Based Seismic Design (PBSD – also called Performance Based Engineering) standards for construction of buildings in earthquake prone regions. Traditionally, all building standards had the design philosophy based on preventing any damage in low-intensity earthquakes, limiting the damage to repairable levels in medium-intensity earthquakes, and preventing the overall or partial collapse of buildings in high-intensity earthquakes. However, several large earthquakes showed that the amount of damage, the economic loss due to downtime, and repair cost of structures were unacceptably high, even though these structures complied with available seismic codes based on traditional design philosophy.

Performance-Based Seismic Design (PBSD) is a methodology which helps in designing buildings according to performance levels classified as a) operational, b) immediate occupancy c) life-safety, and d) collapse prevention, in relation to local hazard levels for events that are categorized as frequent, occasional, rare, and very rare. At the beginning of the design process, the owner and the designer should consult to select a combination of performance and hazard levels and design criteria for each structure based on its function and importance. This method of design can be followed for the most critical structures within the project, even if the local building standards do not cater to performance based engineering.

UTILITIES AND ACCESS: Earthquakes could interrupt the availability and function of off-site utility services such as electricity, water supply, communications, sanitation, as well as access to transportation. Determine potential impacts and provide sufficient on-site back-up and seismic protection of critical utilities. Consider the effects of an earthquake on access to buildings, especially critical buildings (e.g. hospitals) that must be operational immediately following an earthquake.
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Utilities such as power supply, water supply, and sanitation are critical for the continuous functioning of any building in the project. In a strong earthquake, off-site utilities can be disrupted and may remain so for a few days. It is important to ensure that adequate on-site backup is available, and that each critical utility system has been built earthquake resistant. When designing projects in earthquake-prone areas, it is imperative to ensure that the utility systems resist damage due to earthquake shaking. Earthquake shaking can damage electrical equipment, generators and water pumps; break pipelines; and disrupt utility services.

Utility services are interdependent, and damage to one can affect other services as well. Examples include: a) If electrical power is lost, water cannot be pumped; and b) if the access route to the facility is damaged, fuel for the generator cannot be delivered, which will in turn affect the ability to pump water. It is important to understand the criticality of each facility and to address all possible vulnerabilities in the design stage itself, so that the facility can limit disruption due to damage, to one or more of the utility services.

Consider the effects of earthquake forces on the components that form the utility services. Ensure that adequate steps are implemented to limit damage to these critical services by taking steps such as anchoring, bracing and adding flexible connectors. It is also important to estimate how long it would take to repair or reestablish damaged lifeline utilities and to consider the extent to which emergency supplies can meet local needs.

Consider the effects of an earthquake on the access to the buildings under the project, especially if these are lifeline buildings which will be required to be accessed immediately following an earthquake. Road access can be lost by building collapses on to the road, damage to bridges, earthquake induced landslides.

BUILDING CONTENTS AND FALLING HAZARDS MITIGATION: Consider the disruption and damage that an earthquake may cause to buildings and interiors, including windows, doors, furnishings, suspended ceilings and equipment. Design building exteriors so that objects cannot fall on people, especially at exits. Mitigate these hazards during construction to prevent injuries and blockage of exits during earthquakes, and to safeguard essential contents such as medical equipment, sensitive data, or cultural artifacts.
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Interior and exterior finishes, equipment, utility systems (sometimes called “non-structural components” by engineers) and contents can represent 80–90% of the capital investment at risk in commercial, office and residential buildings during an earthquake (Perry et al, 2009). Reconnaissance following earthquakes in a number of countries indicates significant economic losses are the result of damage to architectural elements (such as windows, suspended ceilings and doors), equipment, contents, and building utility systems. Damage to these items in earthquakes can cause deaths, injuries, the building losing ability to function, and economic losses. Any of these non-structural components or contents placed close to exits may block exits and impede evacuations following earthquakes. Thus, constructions in earthquake prone regions require adequate steps to limit damage to these elements in the design stages. The design standards will depend on the functions of the building structure and the nature of the equipment and utilities within the building.

In most countries, non-structural components and the majority of the building contents are not covered by building standard provisions and remain vulnerable to earthquake damage. Mitigation solutions for most of these components are available in various manuals published across the world (a few examples below) and can be incorporated in the construction and maintenance phases so that losses due to them are limited.

EMERGENCY MANAGEMENT: Incorporate emergency contingencies in the buildings’ planning and construction, such as well-located emergency exits, fire extinguishers and clear signs to facilitate safe evacuation in the event of crisis. Critical facilities (such as hospitals or emergency operations centers), or projects that provide backup for critical facilities should remain functional after an earthquake. A clear emergency management plan should be drafted and practiced to prepare staff of those buildings for crisis mitigation.
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In addition to all the other recommendations, the design of each building in the project must incorporate emergency evacuation considerations in the planning stage. This includes considering space requirements and information regarding the functions of the building and the needs of its users (for example, critically ill patients’ beds may have to be wheeled out of a Hospital Intensive Care Unit) and their ability to evacuate in an emergency. Incorporate emergency considerations in the buildings’ planning and construction, such as clear circulation areas, well located emergency exits, and clear signage to facilitate safe evacuation in the event of an emergency.
For projects where buildings will have to remain functional following an earthquake (such as hospitals or emergency operations centers), in addition to having the entire building - including structure, finishes and equipment - protected from earthquake damage and providing back-up for critical utilities, a clear emergency management plan should be drafted and practiced to prepare the staff for crisis mitigation.

Other recommendations for High earthquake prone regions include a. Understanding the earthquake history of the region b. The adequacy of local building regulations c. Understanding the site and soil conditions at the project area d. Ensuring adequately experienced and qualified technical personnel are involved in the design and construction e. Setting standards for design of project buildings depending on the importance of the building’s functions f. Ensuring that utility supplies such as electricity, water supply etc are built earthquake resistant g. Reducing the risk due to damage to architectural elements and building contents in an earthquake and h. Purchasing adequate earthquake insurance to cover potential losses on the project.

INSURANCE: Consider purchasing earthquake insurance to cover potential losses to the project. While insurance does not prevent injuries or deaths, or save communities, it can reduce financial losses and enable a project or facility to recover from the effects of an earthquake and regain its function more quickly.
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Consider purchasing earthquake insurance to cover potential losses on the project. Earthquake insurance may be available from the government or from private insurers. Insurance can help provide funds after an earthquake, to help in reconstruction and replacement of damaged buildings, contents or other project components. This can ultimately enable the project to recover from the effects of the earthquake and regain its function more quickly. However, it is important to note that insurance only provides coverage for financial losses, but cannot prevent damage, business interruption, injuries or deaths.